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SURVEY OF U.S. MINERAL AND METAL PROCESS - page 5 / 12

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includes crushing, dense-medium separation, grinding, froth flotation, and drying of concentrates [

91, [ lo].

Furnace

1

Reverb Furnace

Copper Matte

KEY

Furnace

+

Antimonial Lead

4 Desilverizing

1

bore

Figure 2. Lead mining operations and by-product recovery opportunities

Slag

waste

Sinter oxidation using a blast furnace is the major method for producing lead from sulfide concentrate. In the past two decades, oxygen metallurgy processes have advanced to industrial applications that feature sulfide oxidation in a flash flame or by oxygen injection into a slag bath, followed by reduction of the lead oxide slag [

111.

One type of sintering roaster uses downdraft airflow to produce roasting gases with a concentration of l-2 vol % sulfur dioxide. Gases are recirculated until acid-strength gas is produced. In this system, the molten lead flows downward through the sinter bed with the gas stream. Another type of roaster uses updraft airflow-sintering occurs in an ascending gas stream. A major problem for roaster operations is dust collection because high volumes of ventilation air are handled at considerable cost. Dust recovered from baghouses and wet scrubbers must be recycled to the process. The dust from sintering operations is usually collected in high-temperature electrostatic precipitators. Rich gas containing -6 vol % sulfur dioxide can be delivered to a sulfuric acid plant. Flue dust from lead sintering plants contain

lead, about 10% sulfur, and varying amounts of zinc, cadmium, arsenic, antimony, and mercury. Flue dusts are recycled to the sinter bed.

60-70%

The second part of the roast-reduction process is carried out in a blast furnace. The lead is mostly ‘oxidized with coke. The sinter is charged to the blast furnace and metals are reduced to

.

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